The present technology relates to a secondary battery that includes a cathode, an anode, and an electrolytic solution, and a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus each of which uses the secondary battery.
Various electronic apparatuses such as mobile phones and personal digital assistants (PDAs) have been widely used, and it has been demanded to further reduce size and weight of the electronic apparatuses and to achieve their longer lives. Accordingly, batteries, in particular, small and light-weight secondary batteries that have ability to achieve high energy density have been developed as power sources for the electronic apparatuses.
Applications of the secondary batteries are not limited to the electronic apparatuses described above, and it has been also considered to apply the secondary batteries to various other applications. Examples of such other applications include: a battery pack attachably and detachably mounted on, for example, an electronic apparatus; an electric vehicle such as an electric automobile; an electric power storage system such as a home electric power server; and an electric power tool such as an electric drill.
There have been proposed secondary batteries that utilize various charge and discharge principles in order to obtain battery capacity. In particular, attention has been paid to a secondary battery that utilizes insertion and extraction of an electrode reactant and a secondary battery that utilizes precipitation and dissolution of an electrode reactant, which make it possible to achieve higher energy density than other batteries such as a lead-acid battery and a nickel-cadmium battery.
The secondary battery includes a cathode, an anode, and electrolytic solution. The electrolytic solution includes an electrolyte salt and any other material. The composition of the electrolytic solution exerts a large influence on battery characteristics. Accordingly, various studies have been conducted on the composition of the electrolytic solution.
More specifically, in order to stably maintain capacity for a long time, a cyano borate compound is used as an electrolyte salt (for example, refer to PTL 1). In order to suppress a decline in battery performance over time, a borate compound is used as an electrolyte salt (for example, refer to PTL 2).